A polysaccharide derivative antigen composed of a backbone of repeating alpha-D-Glc-(1->3)-alpha-L-Rha-(1->2)-alpha-L-Rha-(1->3)-alpha-L-Rha-(1->3)-beta-D-GlcNAc units that are connected via beta-(1->2)-linkages between the GlcNAc and the Rha residue adjacent to Glc.